1. Field of the Invention
The present invention relates to network systems, communication apparatus, and communication control methods wherein various kinds of information is transmitted, for example, through radio signals, among a plurality of communication terminals.
2. Description of the Related Art
Conventionally, a network system, for example, in which wireless transmitters are incorporated in personal computers or audio-video devices so as to transmit information among these plural personal computers or audio-video devices is known. In such network system, employed generally is a method in which various types of transmission managements are performed under the control of one central control station, and a plurality of terminal stations are controlled. In this case, a communicating station operating as a control station is set so as to subordinate other communicating stations to the control station to form a network while employing a plurality of wireless communication devices.
In the case where a network is formed employing a plurality of wireless communication devices, a wireless communication control method and the like has been considered wherein a predetermined wireless communication device is specified as the control station of the network, and, for example, a periodic transmission frame cycle is set, or access control of an information transmission region is performed, based on the control of the control station.
In recent years, a wireless communication device has been developed wherein so called an adhoc wireless network can be constructed in which a specific wireless communication device is not determined as the control station from the beginning, and an arbitrary wireless communication device is set as the control station of the wireless network as the need arises so that information can be communicated without any access points. For example, in Japanese Patent Application Laid-Open No. 2000-082989, disclosed is a wireless communication method where so called an adhoc wireless network is constructed in which information can be communicated without any access points while a control station mode and a terminal station mode are switched alternately.
However, in this conventional network system, it is supposed that some inconvenience occurs in a central control station, and the function of the central control station is damaged. In this case, in the conventional network system, a necessity occurs wherein the operating condition of the network is once reset, and another terminal station becomes the central control station so that a wireless network is newly constructed once again. Thus, in the conventional network system, in order to perform this reset (reconstruction of the new wireless network), data transmitted on the network operating so far is temporarily suspended, taking an enormous time period until the network is operated once again.
In order to solve the problem, in Japanese Patent Application Laid-Open No. 2000-151618, the present applicant has proposed a system in which another terminal station in the network is operated as a central control station automatically when some inconvenience occurs in the central control station (master control station) in the network. In this proposed system, the central control station needs to specify in advance a terminal station which would be the central control station when an inconvenience occurs in the master control station as a slave control station. However, for example, in a case where a common power supply is employed for the master control station and the slave control station, when only one slave control station is prepared in the network, and when an inconvenience occurs in both stations at the same time, such problem cannot be dealt with.